This invention relates to enclosure systems for vibratorily driven, sound producing membranes and more particularly relates to a system for minimizing the effect of backwaves generated by such vibrating membranes.
Various sound producing generators such as audio speakers and other audio transducers as well as industrial sound annunciators, such as horns and buzzers, operate by driving a membrane in physical vibrations. The vibrating membrane radiates oppositely directed waves consisting of alternate regions of increased and decreased pressure. Unfortunately, these frontwaves and backwaves can be transmitted through the air to intersect and cause interference, particularly destructive interference.
The conventional approach toward the solution of this problem has been to mount the vibratorily driven membrane at a port provided in the wall of an enclosure. The enclosure is then designed either to eliminate the backwaves by absorbing their energy within the enclosure or to direct the backwaves through passageways and baffles and then transmitting them out of the enclosure in a manner intended to provide only constructive interference with the frontwaves.
One problem with the first mentioned solution is that a substantial amount of energy which is required to drive the vibrating membrane is wasted by subsequent absorbtion in the enclosure. Another problem which increases as a speaker and enclosure becomes smaller is that substantial back pressures are exerted against the vibrating membrane by the gas, usually air, within the enclosure. The back pressure retards the movement of the membrane.
A problem with the second described reflex system is that they are frequency responsive and consequently constructive interference cannot be uniformly maintained over the broad spectrum of audio frequencies.
There is, therefore, a need for an enclosure system for use with vibratorily driven membranes which can dissipate or destroy the backwaves without significant pressure variations within the enclosure in order to minimize the speaker input energy required to overcome these backwaves.